1. Field of the Invention
The present invention relates to a complementary metal-oxide semiconductor (CMOS)-based planar type avalanche photo diode (APD) and a method of manufacturing the same.
2. Description of the Related Art
An avalanche photo diode (APD) indicates a diode using an avalanche phenomenon, in which a layer forming a high electric field in a middle of the diode is required. The layer is called as an embedded junction.
In a conventional APD, the embedded junction is formed by high energy ion implantation. In this case, damages in a silicon lattice occur due to high energy ion implantation, which cause a current leakage, thereby deteriorating breakdown voltage characteristics.
Accordingly, since a conventional silicon APD uses a double side process, it is difficult to manage the conventional APD. In the high energy ion implantation process, damages in a silicon lattice is caused, which are difficult to be adjusted.
The conventional silicon APD will be described with reference to FIG. 1.
FIG. 1 is a cross-sectional view illustrating an APD manufactured according to a conventional method. Referring to FIG. 1, the conventional APD includes a substrate 1-1, an embedded junction 1-2 having junctions 1-2a and 1-2b with the substrate 1-1, a doping area 1-3 having a p-n junction 1-3a, an oxide layer 1-4, a positive electrode 1-5, and a negative electrode 1-6.
In detail, the substrate 1-1 generally uses an n-type silicon substrate rather than a p-type silicon substrate since mobility of electrons greater than that of holes in the APD.
The embedded junction 1-2 is for obtaining avalanche multiplication, and the embedded junction 1-2 is formed by high energy ion implantation and an intermediate layer having a different impurity concentration type from that of the substrate 1-1.
The doping area 1-3 has the p-n junction 1-3a forming a carrier of the APD and is formed by high does ion implantation.
The oxide layer 1-4 is a silicon oxide layer.
The positive electrode 1-5 and the negative electrode 1-6 are formed on a front surface and a rear surface of a wafer, respectively, which are electrodes of the APD. In this case, for ohmic contact to form an electrode on the rear surface, ions having the same type as the substrate 1-1 are implanted into the rear surface. For this, the wafer has to be turned upside down, which is troublesome.
Due to the double side process, it is difficult to manage conventional APDs. Also, conventional methods of manufacturing a CMOS device include forming an n-well and a p-well, setting an active area, and forming a gate oxide layer. Accordingly, when attaching a CMOS circuit to the APD, respective diodes thereof are formed separately from each other and connected to a circuit, which is troublesome.